Effect of Solanum dubium Fruit (Gubbain) Extract on the Milk Clotting and Quality of White Cheese (Gibna Bayda)

Abstract

Two experiments were carried out to study the effect of Solanum dubium fruit extract on weight loss, chemical composition, microbiological quality and sensory characteristics of white cheese (Gibna Bayda) during storage. In the first experiment, Solanum dubium fruit enzymes were characterized. The result showed that the fruit extract of Solanum dubium extract reached its maximum enzyme activity when the fruits were dark yellow in colour and completely dry. Maximum milk clotting activity was obtained by using freeze-dried extract. The loss in activity of the fruit liquid enzyme as well as solid enzyme form increased significantly at room temperature storage compared to refrigerator storage. Subjecting the extract to 70◦C for 10 minutes showed no detrimental effect on its milk coagulating activity. The extract activity was completely destroyed when subjected to 80◦C for 20 minuets.The saturation with ammonium sulphate (60%) gave high milk- clotting activity (5.03 mg/ml) as well as protein content. The partially purified extract had the highest enzymatic activity at 70◦C and pH 10. In the second experiment, the partially purified extract was used in making white cheese. The results indicated that both storage period and salt concentration had significantly affected weight loss and chemical composition of the cheese during storage. Type of milk coagulant (chymosin and Solanum dubium fruit extract) had significant effect on weight loss, total solids, fat, protein, soluble protein, salt, tyrosine and tryptophan. However, it had insignificant effect on titratable acidity and ash contents. Addition of calcium chloride has significantly (P<0.05) affected weight loss, total solids, titratable acidity, ash, and salt of the cheese, and gave insignificant effect on fat, protein, soluble protein, tyrosine and tryptophan. Microbiological quality of cheese samples was significantly affected by storage. Type of coagulant and salt level significantly affected flavour, texture, and saltiness of cheese samples. However, there was insignificant effect on colour of cheese samples. The chemical composition (total solids, fat, titratable acidity, protein, salt and ash contents) of whey from cheese making was significantly affected by storage. Solanum dubium fruit extract may be used as a substitute for rennet enzyme.